PROJECT SUMMARY Women giving birth in the US are 50% more likely to deliver preterm compared to women in Canada or the United Kingdom. The US's high rates of adverse pregnancy outcomes have changed little over time, despite public health and policy programs aimed at increasing access to prenatal care in an effort to reduce rates of adverse pregnancy outcomes. One explanation for the relatively small impact of such efforts is that prenatal care often begins too late to reduce the negative effects of factors such as smoking, alcohol use, obesity, chronic disease, and unintended pregnancy. There is growing recognition that improving women's health prior to conception is key to decreasing rates of adverse pregnancy outcomes. A recent program with the potential to improve women's preconception health is the 2014 Medicaid expansion that occurred under the Affordable Care Act (ACA) but was adopted only in certain states. This program increased access to and utilization of health care services that can improve preconception health (i.e., testing, diagnosis, and treatment for diabetes and high blood pressure and prescription medications for smoking cessation) among low-income adults. The overall goal of this proposal is to assess the impact of the ACA Medicaid expansion on preconception health, reproductive health behaviors (e.g., contraception, unintended pregnancy, and fertility), pregnancy health, and birth outcomes. The first aim of the proposed work is to assess the impacts of the 2014 Medicaid expansion on indicators of preconception health care utilization, health behavior, and health among low-income women 18 to 44 years of age. The second specific aim is to quantify the impact of the Medicaid expansion on reproductive health behaviors including contraception, unintended pregnancy, and fertility. The third specific aim is to ascertain, among women who become pregnant, whether the expansion decreased the probability of 1) maternal pregnancy complications (pregnancy hypertension, eclampsia, and gestational diabetes) and 2) adverse birth outcomes (preterm birth and small weight for gestational age). To achieve our aims, we will link and analyze several large, national data sources and take advantage of the unique opportunity afforded by the inter-state variation in 2014 Medicaid expansion to test the hypothesis that providing health insurance to low income women prior to conception can improve preconception health and thus reduce the prevalence of pregnancy complications and adverse outcomes. The proposed research shifts the paradigm from one focused primarily on women's health during pregnancy to one focused on health prior to pregnancy. The evidence from the proposed research has the potential to shift public health policy toward expanding coverage to low income women of reproductive age in order to improve their preconception and pregnancy health, and thereby reduce preterm birth.